Engine combustion using gasoline fuel may generate particulate matter (PM) (such as soot and aerosols) that may be exhausted to the atmosphere. To enable emissions compliance, particulate filters (PF) may be included in the engine exhaust to filter out exhaust PMs before releasing the exhaust gas to the atmosphere. Such devices may be periodically or opportunistically regenerated during operation of an engine to decrease the amount of trapped particulate matter. In order to effectively schedule PF regeneration, the soot load on the PF is desired to be measured at the onset and during a drive cycle.
Various approaches are provided for accurately estimating soot load on the PF. In one example, as shown in U.S. Pat. No. 8,478,565, Ardanese et al. disclose a method for monitoring soot load on the PF during engine operations while taking into account inefficiency of active regeneration processes. The soot load on the PF is monitored based on operating conditions including differential exhaust pressure across the PF, exhaust temperature, time at which the exhaust temperature is measured, oxygen level, number of previous consecutive incomplete regenerations, and driving mode.
However, the inventors herein have recognized potential disadvantages with the above approach. As one example, in order to monitor soot load on the PF during engine operations, an accurate estimation of soot load at the onset of the drive cycle is desired. Oxidation of accumulated soot on the PF may occur during engine non-combusting conditions, and this oxidation of soot is not accounted for in prior approaches for soot load estimation resulting in inaccurate soot load estimates. If the initial soot load estimate at the onset of a drive cycle is erroneous, PF soot load estimated during the drive cycle may not be accurate, thereby increasing the possibility of reaching higher than desired exhaust backpressure levels which may adversely affect engine output. PF regenerations may be scheduled based on inaccurate soot loads which may result in increased frequency of PF regenerations with a resultant loss in fuel economy. Also, deceleration fuel shut-off (DFSO) events may be altered to inaccurately schedule PF regenerations which may reduce fuel efficiency.
In one example, the issues described above may be addressed by a method comprising: estimating soot loading of a particulate filter (PF), coupled to an exhaust of an engine, during an engine shutdown period to account for soot oxidation during the engine shut down period based on a temperature of the PF at shutdown and a corresponding temperature profile of the PF during the engine shutdown period. In this way, by estimating an amount of soot burned during an engine non-combusting condition, the soot load at the beginning of an immediately subsequent engine combusting condition may be accurately estimated.
As one example, immediately prior to an engine shutdown, an initial PF temperature and an initial soot load on the PF may be estimated based on engine operating conditions and inputs from engine sensors including the exhaust temperature sensor and the exhaust pressure sensor. If it is determined that the PF temperature is higher than a threshold PF temperature, the controller may estimate an amount of soot burned during the engine non-combusting condition. A rate of change of PF temperature during the engine non-combusting condition may be estimated either based on inputs from the exhaust temperature sensor or based on a temperature model. A rate of change of PF soot load during the engine non-combusting condition may be estimated based on each of the initial PF temperature, the rate of change of PF temperature, and the amount of oxygen flowing via the PF. The amount of soot burned during the engine non-combusting condition may be estimated based on the initial PF soot load, the rate of change of soot load, and the duration of the engine non-combusting condition. During an immediately subsequent engine restart, the amount of soot remaining on the PF may be updated based on the initial soot load on the PF and the amount of soot burned during the engine-off period.
In this way, by monitoring changes in soot load during an engine-off period, an accurate estimation of PF load may be obtained at the beginning of an immediately subsequent engine cycle. By modeling and/or measuring change in PF temperature during the engine-off period, an amount of soot burned during this period may be estimated. The technical effect of accurately estimating PF load at the beginning of a drive cycle is that PF regeneration may be scheduled without adversely affecting engine performance caused by undesired exhaust back pressures. By improving the scheduling for PF regeneration, engine conditions such as DFSO may be opportunistically carried out, thereby increasing fuel efficiency. Overall, by monitoring PF load during an engine-off period, PF soot removal during an immediately subsequent drive cycle may be effectively managed thereby improving emissions quality, and fuel economy.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.